JPH03159390A - Chrominance signal output circuit - Google Patents

Abstract

PURPOSE:To eliminate the necessity of an input terminal exclusive for a blanking signal by fetching the blanking signal for character display, etc., by using a primary color signal input terminal for character display, etc. CONSTITUTION:First-third amplifiers 34-36, to which primary color signals are impressed from first-third primary color signal input terminals 4-6, are not operated when the primary color signal is less than a prescribed value, and linear amplification is executed at more than the prescribed value. The blanking signal from an external part is added from a terminal 28 to the third primary color signal input terminal 6. When the voltage of the input terminal is less than a prescribed value and within a prescribed range, first-third switches 10-12 are changed over by the output of a comparator 32 and the output signals of the first-third amplifiers 34 and 36 are selected. Thus, when forming a circuit to an IC, the necessity of one external fitting pin for fetching the blanking signal can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to a color signal output circuit for a TV (television) receiver, particularly for displaying channels and characters on a television screen. The present invention relates to a color signal output circuit for a TV receiver.

(Example) Conventional technology TV receivers that are able to display channels and characters on the screen of TV receivers receiving TV broadcasts use color difference signals demodulated from the TV broadcasts and display signals from the microcontroller. The primary color signals are switched and output. The switching is performed by a blanking signal from the microcomputer, and the primary color signal for display is output in response to the generation of the blanking signal. FIG. 2 shows such a color signal output circuit, which includes first to third color difference signal input terminals (1) to (3) to which color difference signals demodulated from television broadcasting are applied.
>, first to third primary color signal input terminals (4) to (6) to which primary color signals for various displays from the microcomputer are applied;
The first to third amplifiers (7) to (9) and the first to third amplifiers (7) to (9) that selectively output the output signals of the first to third amplifiers (7) to (9) and the first to third color difference signals. Switch (10
) to (12), a fourth switch (15) for selectively outputting the luminance signal from the luminance signal input terminal (13) and the reference voltage from the reference power supply (14) indicating the luminance signal level; A blanking signal input terminal (1
6> and a subtraction circuit that subtracts the color difference signal and luminance signal (
17).

In FIG. 2, when normal TV broadcasting is being demodulated, no blanking signal is generated from the microcomputer, so the blanking signal input terminal 16) is at ground potential, and the first to third switches (16) ) to (12) and the fourth switch (15) are switched to the side shown. Therefore, ( R
-Y), (G-Y) and (BY) color difference signals are the first
The luminance signal from the luminance signal input terminal (13) is sent to the fourth output terminal (21) to the third output terminals (18) to (20).
can be obtained. Each color difference signal is subtracted from a luminance signal outside the IC (22) indicated by a solid line, and becomes a primary color signal, which is supplied to a cathode (not shown) of a cathode ray tube. The subtraction circuit (17) is a part of it, and the B primary color signal is obtained at the output terminal <23). Next, in the above state, if you want to display characters etc. on the screen, a 5 [V] blanking signal from the microcomputer is applied to the blanking signal input terminal (16), and the first
Switch the 3rd to 3rd switches (10 to 12) and the 4th switch (15) in the opposite direction as shown. Therefore, each primary color signal of R.G, B for display from the microcomputer is changed to the first to third primary colors. In addition to the signal input terminals (4) to (6), the first to third
After being amplified by amplifiers (7) to (9), the first to third
It is obtained from the first to third output terminals (18> to <20>) via the switches (lO) to (12).Therefore, a signal corresponding to the ratio of the R, G, and B primary color signals mentioned above is displayed on the screen. It is possible to perform color display, and it is possible to perform a desired display on a normal broadcasting screen. (C) Problems to be Solved by the Invention However, in the circuit shown in The first to third primary color signal input terminals (4) to (6) are used to input R, G, and B primary color signals into the IC (22).
) In addition to this, a dedicated input terminal (l6) is required to take in the blanking signal, resulting in an increase in the number of external pins for the IC (22). (2) Means for Solving the Problems The present invention has been made in view of the above points, and includes first to third color difference signal input terminals to which color difference signals are applied, and a first color difference signal input terminal to which primary color signals are applied. to the third primary color signal input terminal, and the first
first to third amplifiers that stop operating when each primary color signal from a third primary color signal input terminal is less than a predetermined value and perform a linear amplification operation when it exceeds a predetermined value; and the first to third color difference amplifiers. first to third switches for selectively outputting the color difference signal from the signal input terminal and the primary color signals output from the first to third amplifiers; and a reference power supply for indicating the luminance signal from the luminance signal input terminal and the luminance signal level. a fourth switch that selects and outputs the reference voltage of the third primary color signal; and a fourth switch that detects that the terminal voltage of the third primary color signal input terminal is less than or equal to the predetermined value and within a predetermined range; and a comparator for switching three switches, and the first to third switches are switched by applying a blanking signal to the third primary color signal input terminal.

(*> Effect) According to the present invention, the operation of the first to third amplifiers to which the primary color signals from the first to third primary color signal input terminals are applied is disabled when the primary color signals are below a predetermined value. , linear amplification is performed above the predetermined value. Then, a blanking signal is applied from the outside to the third primary color signal input terminal, and when the voltage at the input terminal is below the predetermined value and within a predetermined range. The first to third switches are switched to select the output signals of the first to third amplifiers.

(f) Embodiment FIG. 1 shows an embodiment of the present invention, in which (24) is composed of first to third resistors (25) to (27), and a blanking signal is connected to the terminal (28). The first voltage dividing circuit to which the B primary color signal is applied to the terminal (29>), (30) and (31) the second and third voltage dividing circuits, and (32) the output of the third primary color signal input terminal (6) Voltage and reference voltage V of reference power supply (33)
ref. The first to third switches (10) to (12) and the fourth switch (1
5), and (34) to (36) are the first to third comparators whose operation is switched according to the level of the primary color signal.
It's an amplifier.

In FIG. 1, circuit elements that are the same as those in FIG. 2 are designated by the same reference numerals, and their explanations are omitted. In Figure 1,
When demodulating normal TV broadcasting, the process is almost the same as the case shown in Figure 2, and since no blanking signal is generated from the microcomputer, the third primary color signal input terminal (6) becomes the ground potential, and the comparison output of the comparator (32) becomes the r L level.The first to third switches (10) to (12) and the fourth switch (15) are switched to the side shown in the figure in response to the "L" level signal.As a result, the As in the case of Fig. 2, a primary color signal is obtained at the output terminal of the subtraction circuit <17>.By the way, the first to third amplifiers (34) to (36>
It has the configuration as shown in the figure, and the input signal from the input terminal (37) and the reference voltage Vref of the reference power supply (39) of the comparator (38). A comparison is made with the comparison output, and the switch (40>) is switched in accordance with the comparison output.

Let the value of the reference voltage V ref * be 2 [v], and the voltage f
The output voltage of i (41) is 4 [V], and the input terminal (3
When the voltage of 7) is gradually increased, the input/output relationship becomes as shown in FIG. That is, while the input voltage is up to 2 [V], a fixed voltage of 4 [V] is output, and when it exceeds 2 [V], a nonian amplification operation is performed. Therefore, the minimum level of the primary color signals applied to the first to third primary color signal input terminals (4) to (6) should be set to 2 [V].This will linearly amplify the primary color signals. The desired mixing ratio can be ensured when displaying on the screen.

In FIG. 1, a case will be described in which only a blanking signal is taken in and the screen is blanked. The first resistor <25>, the second resistor (26>) of the first voltage divider circuit (24),
and the resistance values of the third resistor (27) are all set to 4KΩ,
Assume that a blanking signal of 5 [V] is applied to the terminal (28). Then, the voltage of the third primary color signal input terminal (6) becomes 1.6 (V), and the voltage of the third primary color signal input terminal (6) becomes 1.6 (V). 32) is applied to the humidifier (32).
Since the reference voltage V ref is set to 1 [V], the comparison output becomes rH'' level and the first to third switches (
10) to <12> and the fourth switch (l5) are switched in the opposite direction as shown in the figure.On the other hand, for the third amplifier (36),
Since the level is less than 2 [V], the output voltage is the fourth
As shown in the figure, it is 4 [v]. Similarly, since the potentials of the first and second primary color signal input terminals (4) and (5) are grounded, the outputs of the first and second amplifiers (34> and (35) also become 4 [V]. Therefore, 4 [V] is applied to the base of the transistor (42) of the subtraction circuit (17), and the reference voltage Vref (3V) from the reference power supply (14) is applied to the base of the transistor (43). Then, both transistors (42) and (43) are depleted, and the voltage at the output terminal (23) rises to the power supply voltage (10B).In this case, the screen becomes black.In the example of Fig. 1, B Although only the subtraction circuit (17) used for signals is shown, a similar subtraction circuit may be prepared for R and G signals as well.

Next, when displaying characters, apply 5[V to the terminal (28).
] to the terminal (29) with a B of 5 (V).
Apply primary color signals. Then, the third primary color signal input terminal (
The voltage of 6> is 3.3 (V). Then, the output of the humbrator (32) remains at the r H level, and the third amplifier (36) performs a linear amplification operation, and its output becomes approximately 5.7 (V). Therefore, the transistor The potential difference between the bases of (42) and (43) is approximately 2.
7 (V) and both turn on. Therefore, the output terminal (23
) decreases and can drive a cand (not shown) corresponding to B, producing blue (B).
Moreover, if it is desired to obtain red (R), a blanking signal may be applied to the terminal (28>), and a voltage of 2 [V] or more may be applied to the first primary color signal input terminal (4>).

In the embodiment shown in FIG. 1, a case has been described in which the blanking signal is applied to the third ffl color signal input terminal (6), but the present invention is not limited to this, and the blanking signal is applied to the first and third ffl color signal input terminals (6). It may also be applied to the two primary color signal input terminals (4) and <5). (G) Effects of the Invention As described above, according to the present invention, a blanking signal for character display etc. can be taken in using the primary color signal input terminal for character display etc. It has the advantage of not requiring a dedicated input terminal for signals.
Therefore, it has the advantage of eliminating the need for one external pin when integrated into an IC. In addition, in the embodiment shown in Fig. 1, a case has been explained in which all the primary color signals of R, G, and B are taken in, but it is also possible to take in two types or only one type, and in that case, blanking is performed with 2 pins and 1 pin, respectively. It is possible to capture signals.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional color signal output circuit, FIG. 3 is a circuit diagram showing a specific example of the amplifier shown in FIG. 1, and FIG. Figure 4 is a characteristic diagram showing the characteristics of the circuit in Figure 3. <1)(2)(3)...First to third color difference signal input terminals, (4)(5)(6)...First to third primary color signal input terminals, (10)(11) (12) (15)...1st
to fourth switch, (32)... comparator,
(34) (35) (36) . . . first to third amplifiers.

Claims (2)

[Claims] (1) First to third color difference signal input terminals to which a color difference signal is applied, first to third primary color signal input terminals to which a primary color signal is applied, and each from the first to third primary color signal input terminals. first to third amplifiers that stop operating when the primary color signal is less than a predetermined value and perform linear amplification operation when the primary color signal exceeds the predetermined value; and color difference signals from the first to third color difference signal input terminals;
first to third switches for selectively outputting the output primary color signals of the first to third amplifiers; and a first to third switch for selectively outputting the luminance signal from the luminance signal input terminal and a reference voltage from the reference power supply indicating the luminance signal level. 4 switch, and a comparator that detects that the terminal voltage of the third primary color signal input terminal is below the predetermined value and within a predetermined range, and switches the first to third switches according to the detected output, A color signal output circuit characterized in that the first to third switches are switched by applying a blanking signal to the third primary color signal input terminal. (2) The color signal according to claim 1, wherein the color signal output circuit is built into an integrated circuit, and the first to third primary color signal input terminals are arranged as external pins of the integrated circuit. Output circuit.